The use of computer networks, including the Internet, continues to grow at a rapid pace. This growth includes growth in the number of devices on networks, the types of devices on networks, and the protocols used on networks. One aspect of this growth is the encapsulation of a first protocol in a second protocol. An example of this is the iSCSI protocol (Internet SCSI). iSCSI is an Internet Protocol (IP)-based storage networking standard for linking data storage facilities, developed by the Internet Engineering Task Force (IETF). By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. Because of the ubiquity of IP networks, iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.
While iSCSI has many advantages, previous systems implementing the iSCSI protocol have suffered from problems with I/O (input/output) throughput. A potential cause of this problem results from the fact that iSCSI is typically implemented using a virtual device driver. Conventional SCSI interfaces required a hardware adapter to interface with a SCSI device. In such conventional SCSI implementations, the SCSI host bus adapter (HBA) can signal I/O using a hardware interrupt to a physical device driver (physical because a physical HBA is present). As a result, software that uses SCSI can be notified almost immediately that data has been sent or is available.
Unlike conventional SCSI, iSCSI implementations do not interface with a physical SCSI HBA, rather they interface with a network stack in order to communicate with SCSI devices that reside on an IP network. Because no physical SCSI device is present, there are no interrupts to indicate that data has been sent, or is available. As a result, iSCSI implementations in previous systems have typically relied on a timer expiration to cause a virtual device (virtual because there is no physical SCSI device) driver to be polled to see if data is available. In some instances, the resolution of the timer is ten milliseconds, resulting in relatively large polling intervals. When there are many connections between iSCSI hosts and iSCSI targets, such polling is acceptable. However, when there are relatively few connections, the latency in processing serial commands for a connection caused by the polling can be unacceptably large.
As a result, there is a need in the art for the present invention.